The present invention relates to a chuck. More particularly this invention concerns a three-jaw lathe chuck.
A standard lathe chuck has a body rotatable about a body axis and formed with a plurality of angularly spaced, axially forwardly open, and radially extending jaw guides and with respective secantally extending rack guides crossing the jaw guides. Respective jaws are radially displaceable in the jaw guides between radial inner and outer end positions and have axially backwardly directed jaw teeth. Respective racks secantally displaceable in the rack guides each have axially forwardly directed teeth meshable with the respective jaw teeth. The jaw teeth typically extend perpendicular to the respective guide while the rack teeth are angled to the respective rack and parallel to the respective jaw teeth. An actuator jointly displaces the racks secantally in their guides so as to move the jaws radially in their guides.
It is standard to change the jaws to accommodate different workpieces and perform different turning operations. To this end the racks are slid so as to move the jaws to outer end positions in which the jaw teeth disengage from the rack teeth. Then the jaws can be pulled radially out of their guides and new jaws can be pushed radially in to replace them.
The problem is ensuring that a jaw is engaged with enough rack teeth. If only one tooth is engaged, the hold is weak and the tooth can shear off, sending the jaw flying and releasing the workpiece. It is fairly difficult to determine just how well a jaw is engaged when installing it.
It is therefore an object of the present invention to provide an improved lathe chuck.
Another object is the provision of such an improved lathe chuck which overcomes the above-given disadvantages, that is which allows the user to readily determine that a new jaw is engaged by a sufficient number of teeth.
A lathe chuck has according to the invention a chuck body rotatable about a body axis and formed with a plurality of angularly spaced, axially forwardly open, and radially extending jaw guides and with respective secantally extending rack guides crossing the jaw guides. Respective jaws are radially displaceable in the jaw guides between radial inner and outer end positions and have axially backwardly directed jaw teeth. Respective racks are secantally displaceable in the rack guides, and respective bolts in the racks each have axially forwardly directed teeth meshable with the respective jaw teeth and are each displaceable axially between a forward meshing position with the respective jaw and bolt teeth meshed and a rear out-of-mesh position with the respective jaw and bolt teeth out of mesh. A slide assembly angularly displaceable in the body has respective cam surfaces engageable with the bolts. The slide assembly is displaceable angularly between a holding position retaining the bolts in the respective meshing position and a freeing position allowing the bolts to move into the respective out-of-mesh positions. In accordance with the invention respective pins axially displaceable on the bolts have outer ends engageable with the respective jaws in both the meshing and out-of-mesh positions of the respective bolts and respective springs urge the pins axially outward toward the respective jaws.
Thus with this system, as a new jaw is being installed, its teeth will ratchet over the respective pin, producing a clicking sound. This makes it very easy for the person refitting the chuck to determine just how many teeth are engaged and, since the pin will naturally seat between adjacent jaw teeth, will ensure that when the bolts are advanced their teeth will mesh smoothly with the jaw teeth.
The slide assembly and bolts are provided according to the invention with interengaging cam formations for displacing the bolts into the out-of-mesh positions on displacement of the slide assembly into the freeing position. In addition the chuck body is formed with respective axially forwardly open seats receiving rear ends of the bolts in outer positions of the jaws and out-of-mesh positions of the bolts. Thus when the jaws have been moved into their outer positions, which correspond to end positions of the slides, and the bolts have been retracted to the out-of-mesh positions, the chuck is locked. As a result the actuator responsible for displacing the jaws will be held in an end position in which it normally actuates a switch that prevents the chuck from being rotated.
The cam surfaces include surface portions extending perpendicular to the axis and flatly engaging the respective bolts in the meshing positions and immediately thereadjacent angled surface portions. Thus as the slide assembly moves into the holding position from the freeing position the bolts will be smoothly cammed axially forward by the angled surface portions.
The slide assembly includes an angularly displaceable slide body formed with the cam surfaces and at least one rod rotatable in the chuck body and coupled to the slide body for angularly displacing same between the freeing and holding positions. This rod is accessible from outside the chuck so that the user need merely insert a tool into a recess at its outer end and rotate it to free the jaws from the respective bolts, which of course can only happen in outer end positions of the jaws.
The lathe chuck further has according to the invention a drive piston of a power actuator axially displaceable in the chuck body. The racks have angled formations engaged by the drive piston such that axial displacement of the drive piston displaces the racks in the rack guides. This ensures perfectly synchronous movement of the jaws.
The slide assembly can include a plurality of slides and the racks to this end are formed with guide slots slidably receiving the respective slides. Respective springs are braced between the slides and the racks for urging the slides into the holding positions. Alternately the slide assembly includes a ring forming all of the cam surfaces and set in a groove formed in the chuck body.
Respective locking pins according to the invention are axially displaceable in the bolts between forward positions projecting axially forward from the respective bolts and rear positions. The jaws force the locking pins into the rear positions when in mesh with the respective bolts. The slide assembly is formed with respective abutments angularly engageable by the locking pins only in the forward positions so that displacement of the slide assembly is inhibited in the rear positions of the locking pins. More particularly the locking pins have rear ends provided with enlarged heads and the slide assembly is formed with respective slots in which the heads can move angularly in the rear positions and with angularly limited pockets forming the abutments and in which the heads engage in the forward positions. Thus when the jaws are removed the chuck is locked. The locking pins and the pins that ratchet to monitor jaw position can be the same structure.